Polymeric compositions and hydrogels formed therefrom

ABSTRACT

The invention provides new hydrogel forming materials comprising synthetic, hydrophilic, aqueous-insoluble polymer networks formed by copolymerization of a hydrophilic dihydroxyalkyl acrylate or methacrylate, a substantially water insoluble alkyl acrylate or methacrylate, one or more additional hydrophilic comonomers selected from the group of vinylic monomers, acrylates, and methacrylates, and a cross-linking agent. The hydrogels are preferably used for the formation of contact lenses, but may also be used for drug and pesticides delivery devices; dialysis, ultrafiltration and reverse osmosis membranes; implants in surgery and dentistry; and the like.

BACKGROUND OF THE INVENTION

1. Introduction

This invention relates to polymers and hydrogels of polymers formed fromalkyl acrylates or methacrylates, dihydroxyalkyl acrylates ormethacrylates, a third comonomer selected from those hereinafterdescribed, and a cross-linking agent. The polymers absorb water to formhydrogels useful in medical and other applications and are especiallyuseful for the formation of contact lenses.

2. Description of the Prior Art

The synthetic aqueous polymer networks known as hydrogels are threedimensional networks of polymers, generally covalently or ionicallycross-linked, which interact with aqueous solutions by swelling to someequilibrium state. That is, a hydrogel is a polymeric material whichexhibits the ability to swell in water and retain a significant fractionof the imbibed water within its structure. Absent such imbibed water,these materials are properly termed xerogels.

These materials have growing application in the medical field based ontheir bulk and surface properties. They are especially of interest fortheir resemblance to living tissue, for example, in their physicalproperties of high water content and soft, rubbery consistency.

Hydrogel materials are described in U.S. Pat. Nos. 2,976,576 and3,220,960 incorporated herein by reference. These materials, intendedfor use as contact lens materials, are hydrogels of a sparingly crosslinked hydrophilic copolymer and a substantial quantity of an aqueousliquid, e.g. water. The hydrophilic polymer is a copolymer of a majoramount of a polymerizable monoester of an olefinic acid selected fromthe group of acrylic and methacrylic acids having a single olefinicdouble bond and a minor amount of a polymerizable diester of one of saidacids, the diester having at least two olefinic double bonds. Thecopolymer is formed by copolymerization in a solvent medium.

Copolymers that are solvent soluble, but water insoluble formed fromgylceryl methacrylate and methyl methacrylate are known and described byH. Yasuda, C. E. Lamaza, and L. D. Ikenberry, Makromol. Chem. 118, 1935(1968) and H. Yasuda, C. E. Lamaza, and A. Peterlin, J. Polym. Sc. PartA-2, 996, 1117-1131 (1971).

In U.S. Pat. No. 4,056,496, incorporated herein by reference, hydrogelsare disclosed which are suitable for soft lens fabrication. Thehydrogels are formed from a hydrophilic monomer from the group ofdihydroxyalkyl acrylates and methacrylates, a substantially waterinsoluble monomer from the group of alkyl acrylates and methacrylatesand preferably a minor amount of an epoxidized alkyl acrylate ormethacrylate. The dihydroxyalkyl acrylate is preferably used in majoramount, the alkyl acrylate in minor amount, and the epoxidized acrylatein an amount sufficient to impart the desired rigidity. The polymer isformed by a free radical, bulk polymerization process in the substantialabsence of solvent. The materials thus formed are useful after hydrationas soft contact lens material.

Due to the rapidly expanding areas of application of hydrogel materials,new such materials providing improved and/or different physicalproperties are greatly sought after. One particular area of improvementis in the fraction of aqueous solution which can be retained by thehydrogel within its structure. Typically, the higher the water contentof the hydrogel, the poorer the mechanical properties thereof.Nevertheless, higher water content is often desirable, such as formedical applications where high water content is believed to be a majorfactor in the biocompatibility of the hydrogel. Of course, waterinsolubility is essential for most medical application. Accordingly, newmaterials are sought which will retain a greater fraction of aqueoussolution within their structure while having comparable or even improvedmechanical properties.

SUMMARY OF THE INVENTION

The present invention provides a class of new hydrogel forming polymerssuitable for medical and other applications, such as the formation ofcontact lenses, comprising a copolymer of an hydrophilic monomerselected from the group of dihydroxyalkyl acrylate and methacrylates(hereinafter collectively termed "dihydroxyalkyl acrylates"), asubstantially water insoluble monomer selected from the group of alkylacrylates and methacrylates (hereinafter collectively termed "alkylacrylates"), one or more additional monomers selected from the group ofvinylic monomers, and hydrophilic acrylates and methacrylates as furtherdescribed herein, and a crosslinking agent in sufficient quantity toprovide the desired mechanical properties.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

Any hydrophilic dihydroxyalkyl acrylate monomer can be used in thepractice of this invention. Particularly useful, such monomers are thosehaving the following general formula: ##STR1## where R is hydrogen ormethyl and n is a whole integer having a value of from one to four,preferably one or two. Examples of such dihydroxyalkyl acrylates includedihydroxypropyl methacrylates; dihydroxybutyl methacrylates;dihydroxypentyl methacrylates; dihydroxyhexyl methacrylates;dihydroxypropyl acrylates; dihydroxybutyl acrylates; dihydroxypentylacrylates; dihydroxyhexyl acrylates; and the like. A preferreddihydroxyalkyl acrylate is 2,3-dihydroxypropyl methacrylate (glycerylmethacrylate).

The dihydroxyalkyl acrylate can be formed by hydrolysis following theprocedures set forth in British Pat. No. 852,384, incorporated herein byreference. The preferred 2,3-dihydroxypropyl methacrylate may be made bythe process disclosed therein, but is preferably prepared in accordancewith the process described by M. F. Refojo, Journal of Applied PolymerScience, Volume 9, pp. 3161-3170 (1965). This process involves thehydrolysis of glycidyl methacrylate and solvent extraction from thereaction mixture subsequent to the hydrolysis reaction as illustratedbelow.

EXAMPLE 1

One hundred grams of commercial glycidyl methacrylate (American Anilineand Extract Company, Inc.-GMA), 150 ml distilled water and 0.25 ml ofconcentrated sulfuric acid were stirred for six days. During theexperiment, the reaction flask was kept in a water bath at 24°-29° C. Noadditional inhibiting agent was added to the reaction mixture other thanthe amount present in the commercial gylcidyl methacrylate.

Glycidyl methacrylate is immiscible with water, but as the reactionproceeds, solubility is increased until a clear solution is obtained. Asthe reaction proceeds, glyceryl methacrylate is formed whichco-dissolves the unreacted glycidyl methacrylate.

The reaction mixture was neutralized with 10% sodium hydroxide and thenextracted with five 100 ml portions of ether. The ether extract waswashed with three 20 ml portions of distilled water, then this aqueoussolution was washed again with 50 ml of ether. The combined etherextracts were dried with anhydrous sodium sulfate. The ether was thenevaporated in a rotating evaporator with the rotating flask kept in acool water bath. The residue from the ether extract, 18.8 g, was mainlyglycidyl methacrylate which could be used to prepare more glycerylmethacrylate.

The aqueous extract from the ether solution was saturatedd with sodiumchloride. The glyceryl methacrylate separated out as an oily layer abovethe saturated saline solution. The oily material was dissolved inmethylene chloride. The organic solution was dried with anhydrous sodiumsulfate and evaporated, without heating, but using the same proceduredescribed above for the concentration of the ether extract. The residuefrom the evaporation (11.6 g) was a viscous, clear liquid, namelyglyceryl methacrylate.

The aqueous reaction medium, previously extracted with ether, uponsaturation with sodium chloride, separated into two layers. The organiclayer was taken up with methylene chloride and the solution, after beingdried with anhydrous sodium sulfate, was evaporated in the rotatingevaporator by using a cool water bath under the rotating flask. Theyield was 71.6 g of glyceryl methacrylate. This reaction product alsocontained between about 1.8% and 2.2% by weight of unreacted glycidylmethacrylate which was not removed in the extraction step. Minor amountsof other impurities, such as methacrylic acid, glyceryl methacrylatediester and/or glyceryl methacrylate triester, may also have beenpresent.

Other dihydroxyalkyl acrylates can be made in a similar manner.

The second monomer can be any substantially water insoluble alkylacrylate or alkyl methacrylate. Particularly useful such monomers arethose having the general formula: ##STR2## where R' is hydrogen ormethyl and R² is an alkyl group preferably having from about 1 to 6carbon atoms. Alkyl acrylates conforming to this formula are readilyavailable. Examples of suitable such acrylates include methyl acrylate,methylmethacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate,propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butylmethacrylate, and the like, etc. Methyl methacrylate is presentlypreferred.

The third monomer comprises one or more of the following:

(A) A vinylic monomer conforming to the formula: ##STR3## where R³ is ahydrophilic moiety comprising, for example, hydroxyl; alkoxy, preferablyhaving 1 to 6 carbon atoms and more preferably methoxy or ethoxy; anacidic group, such as sulfonic acid moiety; ##STR4## wherein R⁴ and R⁵are independently selected from a hydrogen atom and alkyl or substitutedalkyl groups having from 1 to about 3 carbon atoms, and R⁴ and R⁵ may becombined to form a cyclic group; or ##STR5## wherein R⁴ and R⁵ aredefined as above and may be combined to form a lactam such aspyrrolidone or piperidone; and n is zero to four, except that when R³ ishydroxyl, n must be at least one. Examples of suitable vinyliccomonomers include vinyl acetate, 3-buten-1-ol, 2-propen-1-ol,5-hexenol, methyl vinyl ether, propyl vinyl ether, butyl 3-buten-1-olether, N-methyl vinyl amide, N-propyl vinyl amide, N-ethyl-3-butenamide.A preferred monomer is vinyl pyrrolidone, ##STR6##

(B) Hydrophilic acrylates having the formula: ##STR7## where R⁶ isamido, hydroxyalkoxy, preferably having 1 to 6 carbon atoms, or otherhydrophilic group and R' is hydrogren or methyl as above. Examples ofsuch acrylates include, for instance, 3-hydroxypropyl acrylate,2-hydroxyethyl methacrylate, methacrylamide, N-methyl methacrylate,N,N-dimethyl methacrylamide, and the like, etc. Preferred third monomersinclude 2-hydroxyethyl acrylate, ##STR8## and the acrylamides ##STR9##where R⁷ and R⁸ are independently selected from hydrogen or lower alkylgroups, particularly alkyl groups having 1 to 4 carbon atoms.

(C) Mixtures of monomers described in paragraphs (A) and (B) above.

It will be noted that a common denominator among the three monomers isthe presence in each of an activated carbon-carbon double bond, the siteat which polymerization occurs. A significant shared property, however,is the general ability of the monomers to introduce one or morehydrophilic groups to the polymer network to produce an improvedhydrogel.

The molar ratio of the dihydroxyalkyl acrylate to the alkyl acrylate canvary within broad limits dependent upon the use to which the material isto be put. Preferably, the ratio varies within the range of from about1:3 to about 20:1. Preferably, the dihydroxyalkyl acrylate at leastequals or exceeds the alkyl acrylate and a preferred ratio variesbetween about 1:1 and 10:1. More preferably, the molar ratio is about1.2:1.0 and about 2:1. (For use of the hydrogel as a contact lensmaterial, the most preferred molar ratio is about 1.5:1.0.)

The molar ratio of the third monomer to the total of dihydroxyalkylacrylate plus alkyl acrylate monomers can also vary within broad limitsagain dependent upon the use to which the material is to be put.Preferably, the ratio varies within the range of 1:1 down to anegligible amount of third monomer. The most preferred amount of thirdmonomer used will depend both on the particular monomer selected for useand on the mechanical properties most advantageous to the particularapplication and can be readily determined through a routine series ofpolymerizations over a range of mole ratios.

The cross-linking agent can by any compound having two reactive olefinicdouble bonds. Particularly useful compounds for cross-linking in thisinvention are the divinyl compounds. The cross-linking agent, amongother things, aids in providing desirable mechanical properties to thehydrophilic polymers of this invention and enables them to be insolublein aqueous solutions while imbibing large amounts of such solutions.

As aforesaid, divinyl compounds are particularly useful as cross-linkingagents in the practice of this invention. Preferred divinyl compoundsinclude those compounds having diesters with acrylic or methacrylicacid. Typical examples of such preferred compounds include the glycoldiesters such as, for instance, ethylene glycol dimethyacrylate,propylene glycol dimethacrylate, ethylene glycol diacrylate, and thelike. Other examples of useful cross-linking agents includetriethanolamine dimethacrylate, triethanolamine trimethacrylate,tartaric acid dimethacrylate, triethylene glycol dimethacrylate, thedimethacrylate of bishydroxyethylacetamide, and the like.

The amount of such cross-linking agent is dependent upon obtaining thedesired rigidity. In general, the concentration does not exceed 5% ofthe total monomer constituents, preferably ranges between about 0. 1 to4% and should be in an amount sufficient to yield a hydrogel from thepolymer having the desired hydration properties. Desirably, the amountof cross-linking agent is that necessary to provide a polymer capable ofabsorbing water of hydration in an amount of from about 35 to about 50%by weight and preferably from about 40 to about 46%.

It is believed that epoxidized acrylate acts as a cross-linking agentand may be added in an amount which varies within broad parameters asdiscussed above. Normally an appreciable amount of unreacted epoxy alkylester will remain in the reaction mixture of Example 1 even afterrepeated solvent extraction steps. This is apparently due to thedihydroxyalkyl acrylate acting as a cosolvent for the ester in theaqueous phase. However, if the amount of unreacted ester present in thedihydroxyalkyl acrylate product is different from the amount necessaryin order to get the desired degree of cross-linking, it can be adjustedby addition of epoxy alkyl ester to increase cross-linking or byreducing the amount of ester in the product in order to decreasecross-linking. The amount of ester can be reduced, for example, byfurther solvent extraction steps, as is well known in the art.Generally, the epoxidized acrylate may be added in an amount of from 0to 30% by weight of the dihydroxy acrylate monomer, but more preferably,from 0.1 to 15% by weight and most preferably 1.0 to 7.5%, dependingupon the particular monomers used, their ratio and other factors.

As to the degree of cross-linking of the gels from the polymersdescribed herein, a guide to the extent of cross-linking is thesolubility properties of the gels in various organic solvents. Ingeneral, the gels are insoluble in solvents such as dioxane, acetone,methylene chloride and mixtures thereof.

For use as a contact lens, the hydrogels preferably have certainproperties. The percent hydration with water has been discussed above.Another property is the percent linear elongation. Preferably, thehydrated gel will exhibit a linear expansion of from about 15 to about25% and more preferably, from about 18 to about 21%. A further propertyis the hardness of the material. Preferably, it has a Shore A durometerType A-2 reading (ASTM Designation D2240-68) of from about 40 to about50 and more preferably, from about 42 to about 47.

The polymers are generally formed by bulk polymerization using suitablecatalysts. The monomers are mixed in the absence of solvent andmaintained under reduced pressure at an elevated temperature for aperiod of time sufficient to solidify the reaction mixture. Typically,the temperature of reaction varies between 20° and 60° C. The catalystconcentration may vary within broad limits dependent upon the particularcatalyst used, but generally varies between about 0.0001 and 0.2 weightpercent of the hydroxyalkylacrylate, and preferably between 0.0005 and0.01 weight percent. A wide variety of catalysts are known to initiatethe polymerization reaction and one skilled in the art can select any ofthe known catalysts that are suitable for the particular polymerizationbeing conducted. Preferred catalysts are oxidants such as isopropylpercarbonate and free radical initiators such as azobisisobutyronitrile.

While the uses, medical or otherwise, to which the polymers describedherein may eventually be put is impossible to predict, their ability toretain greater amounts of imbibed aqueous solution while having goodmechanical properties represents a significant advance in the technologyof hydrogels.

Having above generally described the invention, the following exampleswill illustrate specific embodiments.

EXAMPLE 2

The bulk copolymerization of 2,3-dihydroxypropyl methacrylate (GMA) madein accord with Example 1 with methyl methacrylate (MMA) and vinylpyrrolidone was carried out. The amount of 1.14 g of said GMA and 0.27 gof vinyl pyrrolidone and 0.27 g of MMA were mixed together. To themixture was added 1.0 mg of azobisisobutyronitrile as a catalyst. Thecomposition was heated at 80° C. A clear copolymer formed in 10 minutes.

EXAMPLE 3

The bulk copolymerization of GMA made in accord with Example 1 with MMAand methacrylamide was carried out. The amount of 0.5 g MMA and 1.14 gof said GMA and 0.5 g of methacrylamide were mixed and warmed briefly tosolution. To the mixture was added 1.0 mg of azobisisobutyronitrile ascatalyst. The mixture was heated at 80° C. and a clear copolymer formedwithin five minutes.

As noted above, the hydrogels of this invention have properties whichmake them excellent materials for soft contact lens application. Afterabsorbing water (pysiological saline water or water containing aphysiologically active solute such as a bacteriostatic agent) thehydrogels are soft and flexible, but at the same time, they are toughand resist tearing. They are somewhat more rigid than prior artmaterials used for hydrogel contact lenses and consequently, maintainthe contour of the eye to a greater extent than prior art materials andmay be fabricated in thinner cross section. Moreover, the increasedrigidity prevents misshaping by blinking thus preventing an everchangingoptical surface with resulting invariations and distortions of vision.

In addition to the above utility of the copolymers of this invention,the physiochemical properties make them suitable for prolonged contactwith living tissue, blood and mucous membrane such as would be requiredfor surgical implants, blood dialysis devices and the like. In thisrespect, it is known that blood, for example, is rapidly damaged when incontact with most artificial surfaces. The design of a synthetic surfacewhich is antithrombogenic and nonhemolytic to blood is necessary for anyprosthesis end device to be used with blood. The non-ionic hydrogels,such as those of the subject invention, are known to substantiallyreduce the clotting tendency of blood.

The hydrogels are also selectively permeable to water and thus, theyqualify for various applications involving dialysis, ultrafiltration,and reverse osmosis. In this respect, it is particularly advantageousthat the permeability of these hydrogels may be adapted for any desiredpurpose and the size and shape of a diaphragm may be prepared in situ toform an integral part of a hydrophilic article or device. The goodchemical stability of the hydrogels also make them suitable forelectrolytic purposes.

The copolymers of the subject invention can also be impregnated with adrug. Then, when the copolymer, in the form of an article made therefromsuch as an intrauterine device is administered to a patient, the drugwill gradually be released to the patient. As the drug is removed fromthe surface of the coplymer, it will be replaced with a fresh supply ofdrug migrating to the surface of the copolymer from its interior.

In a similar manner, the copolymers may be used for controlled releaseof pesticides. Pesticides, particularly biodegradable pesticides,released gradually by diffusion from the copolymer, when applied in thismanner, will reduce environmental hazards associated with the continuedusage of conventional pesticides.

The entire article prepared according to this invention forms a latticeof giant swollen molecules when immersed in water. It is therefore notonly permeable to water and to certain aqueous solutions, but alsostrong, of stable shape and very elastic. It can be boiled in waterwithout being damaged whereby thorough sterilization may be achieved.These properties make an article formed from the copolymer of theinvention particularly suitable for purposes in surgery, where a bodycompatible with living tissue or with a mucuous membrane may be used,e.g.- for making contact lenses as described above, for filling ordividing cavities in tissue, for pessaries, etc.

While the present invention has been described in detail along with thepreferred embodiments thereof, it is understood that those skilled inthe art may effect various modifications within the spirit and scope ofthis invention.

We claim:
 1. A hydrophilic polymer comprising the polymerization productof:a first monomer comprising a dihydroxyalkyl acrylate, a secondmonomer comprising a substantially water insoluble alkyl acrylate oralkyl methacrylate, the mole ratio of said first monomer to said secondmonomer varying within the range from about 1:3 to about 20:1; a thirdmonomer comprising a compound selected from the group consisting of:##STR10## where R³ is hydroxyl, alkoxy having 1 to 6 carbon atoms, asulfonic acid moiety, ##STR11## wherein R⁴ and R⁵ are independentlyselected from hydrogen and an unsubstituted or substituted alkyl grouphaving from 1 to about 3 carbon atoms, and R⁴ and R⁵ may be combined toform a cyclic group, or ##STR12## wherein R⁴ and R⁵ are as definedabove, and n is an integer from 0 to about 4, except that n must be atleast 1 when R³ is hydroxyl; ##STR13## where R⁶ is hydroxyalkoxy having1 to 6 carbon atoms or --NR⁷ R⁸ where R⁷ and R⁸ are independentlyselected from hydrogen and lower alkyl groups having 1 to 4 carbonatoms; ##STR14## where R⁹ is hyroxyalkoxy having from 1 to about 6carbon atoms; and (d) mixtures thereof:the total of the molar quantitiesof said first and second monmers to the molar quantity of said thirdmonomer being in the range of 1:1 to 1:0.2.
 2. The hydrophilic polymerof claim 1 wherein said polymer has a Shore A durometer Type A-2 readingof from about 40 to about
 50. 3. The hydrophilic polymer of claim 1wherein said polymer is insoluble in a solvent selected from the groupof acetone, dioxane, or mixtures thereof.
 4. The hydrophilic polymer ofclaim 1 wherein said first monomer comprises a compound having theformula: ##STR15## wherein R is hydrogen or methyl and n is an integerfrom 1 to
 4. 5. The hydrophilic polymer of claim 4 wherein said firstmonomer comprises a compound selected from the group consisting ofdihydroxypropyl methacrylate; dihydroxybutyl methacrylate;dihydroxypentyl methacrylate; dihydroxyhexyl methacrylate;dihydroxypropyl acrylate; dihydroxybutyl acrylate; dihydroxypentylacrylate; and dihydroxyhexyl acrylate.
 6. The hydrophilic polymer ofclaim 1 wherein said second monomer comprises a compound having theformula: ##STR16## wherein R' is hydrogen or methyl and R² is an alkylgroup having from 1 to about 6 carbon atoms.
 7. The hydrophilic polymerof claim 6 wherein said second monomer comprises a compound selectedfrom the group consisting of methyl acrylate, methylmethacrylate, ethylacrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate,isopropyl acrylate, isopropyl methacrylate, and butyl methacrylate. 8.The hydrophilic polymer of claim 1 wherein said third monomer isselected from the group consisting of vinyl acetate 3-buten-1-ol,2-propen-1-ol, 5-hexenol, methyl vinyl ether, propyl vinyl ether, butyl3-buten-1-ol ether, N-methyl vinyl amide, N-propyl vinyl amide,N-ethyl-3-butenamide and vinyl pyrrolidone.
 9. The hydrophilic polymerof claim 1 wherein said third monomer comprises a compound selected fromthe group consisting of 3-hydroxypropyl acrylate, 2-hydroxyethylmethacrylate, methacrylamide, N-methyl methacrylamide, N,N-dimethylmethacrylamide, and 2-hydroxyethyl acrylate.
 10. A shaped article madefrom the hydrophilic polymer of any of claims 1 through 5, 6, 7, 8 or 9.11. The shaped article of claim 10 in the form of a contact lens. 12.The hydrophilic polymer of claim 1 wherein said molar ratio of saidfirst monomer to said second monomer is at least 1:1.
 13. Thehydrophilic polymer of claim 1 further including a cross-linking agent.14. The hydrophilic polymer of claim 13 wherein said cross-linking agentcomprises a divinyl compound having two reactive olefinic double bonds.15. The hydrophilic polymer of claim 13 wherein said cross-linking agentis present in an amount less than about 5 mole percent.
 16. Thehydrophilic polymer of claim 13 wherein said cross-linking agent isselected from the group consisting of ethylene glycol dimethyacrylate,propylene glycol dimethacrylate, ethylene glycol diacrylate,triethanolamine dimethacrylate, triethanolamine trimethacrylate,tartaric acid dimethacrylate, triethylene glycol dimethacrylate, and thedimethacrylate of bishydroxyethylacetamide.
 17. The hydrophilic polymerof claim 1 wherein said first monomer comprises a hydrophilic compoundhaving the formula: ##STR17## wherein R is hydrogen or methyl and n isan integer from 1 to 4; said second monomer comprises a substantiallyinsoluble acrylate or methacrylate selected from the group consisting ofmethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate,isopropyl methacrylate, butyl acrylate, and butyl methacrylate; and saidthird monomer is selected from the group consisting of vinyl acetate,3-buten-1-ol, 2-propen-1-ol, 5-hexenol, methyl vinyl ether, propyl vinylether, butyl 3-buten-1-ol ether, N-methyl vinyl amide, N-propyl vinylamide, N-ethyl-3-butenamide, vinyl pyrrolidone, 3-hydroxypropylacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,methacrylamide, N-methyl methacrylamide, N-N-dimethyl methacrylamide,and mixtures thereof.
 18. The hydrophilic polymer of claim 17 whereinsaid first monomer comprises 2,3-dihydroxypropyl methacrylate.
 19. Thehydrophilic polymer of claim 17 wherein said second monomer comprisesmethyl methacrylate.
 20. The hydrophilic polymer of claim 17 whereinsaid third monomer comprises a compound selected from vinyl pyrrolidone,2-hydroxyethyl acrylate or methacrylamide.
 21. The hydrophilic polymerof claim 17 further including a cross-linking agent selected from thegroup consisting of, ethylene glycol dimethacrylate, propylene glycoldimethacrylate, ethylene glycol diacrylate, triethanolaminedimethacrylate, triethanolamine trimethacrylate, tartaric aciddimethacrylate, triethylene glycol dimethacrylate, and thedimethacrylate of bis-hydroxyethylacetamide.
 22. The hydrophilic polymerof claim 17 wherein said first monomer comprises 2,3-dihydroxypropylmethacrylate, said second monomer comprises methyl methacrylate and saidthird monomer comprises a compound selected from the group consisting ofvinyl pyrrolidone, 2-hydroxyethyl acrylate, and methacrylamide.
 23. Thehydrophilic polymer of claim 17 further including a cross-linking agentcomprising glycidyl methacrylate.
 24. The hydrophilic polymer of claim22 wherein said molar ratio of said first monomer to said second monomeris in the range of from about 1:1 to about 10:1.
 25. The hydrophilicpolymer of claim 22 wherein said third monomer comprises vinylpyrrolidone that is present in a molar ratio of 1:1 to 1.0:0.2 whencompared to the total moles of first and second monomers.
 26. Thehydrophilic polymer of claim 22 wherein said third monomer comprisesmethacrylamide that is present in a molar ratio of 1:1 to 1.0:0.2 whencompared to the total moles of first and second monomers.
 27. Thehydrophilic polymer of claim 22 wherein said third monomer comprises2-hydroxyethyl acrylate that is present in a molar ratio of 1:1 to1.0:0.2 when compared to the total moles of first and second monomers.28. The hydrophilic polymer of any of claims 17 through 26 or 27 whereinsaid polymer when hydrated exhibits a linear expansion of from about 15to about 25 percent.
 29. A shaped article made from the hydrophilicpolymer of any of claims 17 through 26 or
 27. 30. A contact lens formedfrom the hydrophilic polymer of any of claims 17 through 26 or 27.